RAID

[Kevin Buettner]

On Aug 8, 11:18pm, Nick Estes wrote:

> On Wed, 8 Aug 2001, Craig White wrote:
> 
> > Philosophical question
> > Budget $500 - Raid level 1 intended
> >
> >  - 2 IBM UltraStar 18.1G Ultra2SCSI, computer has AIC7880 embedded
> > controller but also has CD & Python Tape on it. Software raid (package?)
> >
> > 0r
> >
> >  - 2 Western Digital 30G UDMA with Promise ATA/66 Raid controller
>
> Software raid is quite doable, and I have done a lot of it, but you had
> better know exactly what you're doing when it has a problem.  Plus it's
> much more likely to have a problem since it depends on the system properly
> shutting down to prevent data corruption (you think fsck takes a long
> time? try chkraid)

I have some recent experience with this.  One of the drives in my
Linux software RAID-1 setup failed recently.  Initially, however, I
wasn't sure what the problem was and attempted to reboot with both the
good drive and the failing drive.  On one attempt, the system didn't
even recognize the failing drive; later on, after power-cycling the
box, the system recognized it and it came up.  The linux kernel
correctly recognized that the two were out of sync and correctly
picked the most recently updated drive to use...  I used
``raidhotadd'' to add the partitions from the failing drive back in.

The kernel synchronizes the drives in the background, so you have very
little downtime.  As for ``ckraid'', the man page says that it's
obsolete.  The description from ckraid(8) says

       in  earlier  RAID  versions,  ckraid checked a RAID device
       array for consistency. This work is now all  done  by  the
       kernel.

I don't know why, but sometime after using ``raidhotadd'' to add the
failing (failed?) drive partitions back in, the machine crashed on
me again.  The next day, I put in a replacement drive, created the
necessary partitions, and used raidhotadd to add these to the array.
It worked beautifully.

> My vote is definatly hardware raid with the IDE drives rather than
> software raid with scsi, you'll get more space for your dollar, hardware
> raid works a lot smoother with no software configs to worry about, and
> raid 1 will help the performance of the IDE drives (mainly on reads).

Be careful regarding a vendor's claim of "hardware" RAID.  It is
my understanding that the Promise controllers do not offer true
hardware RAID.  (There are drivers which do the work...)  If you
want a true hardware RAID controller, take a look at the 3ware
Escalade.  See http://www.3ware.com.  (I don't have any experience
with these controllers; take a look at Google Groups first though...)

Now back to Promise...  back when I was researching RAID on Linux, the
Promise RAID cards weren't supported (for RAID) by Linux.  It's my
understanding that they could still be used as an ordinary IDE
controller, however.  I think Promise was working on Linux support and
it the work may be completed now.  You should check on the status
first.  I have a Promise Ultra66 that I'm using with the Linux
software RAID solution above and I really like it.  (Also, see Tom's
hardware for an article which describes how to convert an Ultra66 into
a FastTrak66.)

Kevin